Customarily in packaging machines, for example machines for dispensing metered amounts of a comestible into a cup or for wrapping a metered amount of a substance, the main drive shaft is common to a multiplicity of working stations such as those delivering the cups, feeding the metered quantities of substance into the cups, closing the cups, etc., and each working station has a working-station drive shaft which is to be coupled to or decoupled from the main drive shaft. Such systems may use a single jaw clutch to effect the connection.
In most cases, it is necessary or desirable to reduce the speed of the main drive shaft and hence the cycling time to enable the engagement of a single jaw clutch without significant transmission of shock to the immobile working-station drive shaft or the generation of shock at the main drive shaft as a result of the coupling of the stationary working-machine drive shaft thereto.
A reduction in the speed of the main drive shaft is, however, a significant drawback since it materially reduces cycling time and the machine output. It is conceivable to avoid problems of such impact by overdimensioning the clutch and the clutch surfaces so that they are able to take up the shock of coupling directly. Not only is this an expensive approach, but it requires considerable space which may not always be available.
In German patent document DE-OS 1 600 211a drive using a single-tooth clutch is described in which a friction clutch is also provided to enable the driven shaft to be brought up to speed of the drive shaft utilizing the slip in the friction clutch.
A similar approach is used in German patent document DE-PS 1 161 729.
The provision of friction clutches in packaging machines can present problems of wear and maintenance which best should be avoided. Furthermore, friction clutches may contribute inordinately to the cost of the apparatus.